Driving apparatus having improved engagement

ABSTRACT

A driving apparatus includes a driving input gear with first gear teeth, a columnar shaft, and a driven gear that engages the driving input gear. The driven gear includes a cylindrical boss portion, a cylindrical rim portion, a web, and second gear teeth. The second gear teeth are formed at an outer peripheral surface of the rim portion. The first gear teeth are first helical teeth twisted in a first direction with respect to a direction that the rotary drive shaft extends. The second gear teeth are second helical teeth twisting in a second direction that is the opposite of the first direction. The rim portion is tapered, radially decreasing toward the end to which the web is linked. The through-hole of boss portion has an inner diameter larger than an outer diameter of the shaft.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon, and claims the benefit of priority from,corresponding Japanese Patent Application No. 2013-128345 filed in theJapan Patent Office on Jun. 19, 2013, the entire contents of which areincorporated herein by reference.

BACKGROUND

Unless otherwise indicated herein, the description in this section isnot prior art to the claims in this application and is not admitted tobe prior art by inclusion in this section.

An image forming apparatus includes various rotators. For example, theimage forming apparatus includes a photoreceptor drum on whichelectrostatic latent images and toner images are formed, a developingroller, a drive roller, a conveyance roller, and a similar unit. Thedeveloping roller is to supply the photoreceptor drum with toner. Thedrive roller circularly drives a transfer belt to which the toner imageis to be primarily transferred. The conveyance roller is to convey asheet along a conveyance path. There is a driving apparatus for theseunits that includes a driving motor, a pinion gear (a driving inputgear), and a driven gear. The pinion gear is directly connected to themotor. The driven gear engages the pinion gear.

SUMMARY

A driving apparatus according to the disclosure includes a driving inputgear, a columnar shaft, and a driven gear. The driving input gear has arotary drive shaft and first gear teeth, the rotary drive shaft beingconfigured to receive rotary driving power. The first gear teeth areintegrally formed with the rotary drive shaft. The columnar shaftextends parallel to the rotary drive shaft. The driven gear engages thedriving input gear. The driven gear includes a cylindrical boss portion,a cylindrical rim portion, a web, and second gear teeth. The cylindricalboss portion is wholly made of a resin material, the boss portion havinga through-hole through which the columnar shaft is inserted. Thecylindrical rim portion is disposed concentrically with and outerperipherally of the boss portion. The web links a circumferentialsurface of the boss portion with the rim portion along one end of therim portion axially. The second gear teeth are formed on an outerperipheral surface of the rim portion. The first gear teeth are firsthelical teeth twisting in a first direction with respect to a directionin which the rotary drive shaft extends. The second gear teeth aresecond helical teeth twisting in a second direction that is the oppositeof the first direction. The rim portion is tapered, radially decreasingtoward the end to which the web is linked. The through-hole in the bossportion has an inner diameter greater than the columnar shaft outerdiameter. The rotary drive shaft rotational direction, the firstdirection, and the second direction are established such that, with thedriven gear tilting because of clearance between the through-hole andthe columnar shaft, under thrust power generated by engagement betweenthe first helical teeth and the second helical teeth and transmission ofthe rotary driving power from the driving input gear to the driven gear,the inclination changes the posture of the tapered rim portion so as toparallel the rotary drive shaft.

These as well as other aspects, advantages, and alternatives will becomeapparent to those of ordinary skill in the art by reading the followingdetailed description with reference where appropriate to theaccompanying drawings. Further, it should be understood that thedescription provided in this summary section and elsewhere in thisdocument is intended to illustrate the claimed subject matter by way ofexample and not by way of limitation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an internal structure of an image forming apparatus(a driving apparatus) according to one embodiment of the disclosure;

FIG. 2 illustrates a discharge unit included in the image formingapparatus;

FIG. 3 illustrates a drive transmission device assembled to the sheetdischarge unit;

FIG. 4 illustrates a side of the drive transmission device;

FIG. 5 illustrates a top of the drive transmission device;

FIG. 6 illustrates a cross section of the drive transmission devicetaken along the line VI-VI of FIG. 5;

FIG. 7 illustrates a cross section along an axial direction of areduction gear (a driven gear) according to the one embodiment;

FIG. 8 illustrates a cross section along an axial direction of areduction gear according to a comparative example;

FIG. 9 schematically illustrates a state of engagement between a piniongear and the reduction gear according to the one embodiment; and

FIG. 10 schematically illustrates a state of engagement between thepinion gear and the reduction gear and illustrates the inclinedreduction gear according to the one embodiment.

DETAILED DESCRIPTION

Example apparatuses are described herein. Other example embodiments orfeatures may further be utilized, and other changes may be made, withoutdeparting from the spirit or scope of the subject matter presentedherein. In the following detailed description, reference is made to theaccompanying drawings, which form a part thereof.

The example embodiments described herein are not meant to be limiting.It will be readily understood that the aspects of the presentdisclosure, as generally described herein, and illustrated in thedrawings, can be arranged, substituted, combined, separated, anddesigned in a wide variety of different configurations, all of which areexplicitly contemplated herein.

The following describes an embodiment of the disclosure in detail basedon the drawings. FIG. 1 illustrates a cross section of an internalstructure of an image forming apparatus 1 according to one embodiment ofthe disclosure. Here, as one aspect of a driving apparatus, an imageforming apparatus formed of a tandem color laser printer is exemplified.The image forming apparatus may be a copier, a facsimile device, or amulti-functional peripheral with these functions.

The image forming apparatus 1 includes a main body housing 100. The mainbody housing 100 constitutes an outer body and houses variousapparatuses. The image forming apparatus 1 includes a magenta imageforming unit 1M, a cyan image forming unit 1C, a yellow image formingunit 1Y, a black image forming unit 1Bk, an intermediate transfer unit11, toner containers 12 a to 12 d, an exposure unit 13, and a sheet feedcassette 14 in the main body housing 100. The magenta image forming unit1M, the cyan image forming unit 1C, the yellow image forming unit 1Y,and the black image forming unit 1Bk are tandemly located at constantintervals. The intermediate transfer unit 11 and the toner containers 12a to 12 d are located above these image forming units 1M, 1C, 1Y, and1Bk. The exposure unit 13 and the sheet feed cassette 14 are locatedbelow these image forming units 1M, 1C, 1Y, and 1Bk.

The image forming units 1M, 1C, 1Y, and 1Bk include photoreceptor drums2 a, 2 b, 2 c, and 2 d, respectively. Around the photoreceptor drums 2a, 2 b, 2 c, and 2 d, charging rollers 3 a, 3 b, 3 c and 3 d, developingdevices 4 a, 4 b, 4 c, and 4 d, primary transfer rollers 5 a, 5 b, 5 c,and 5 d, and drum cleaning apparatuses 6 a, 6 b, 6 c, and 6 d arelocated, respectively. Since the respective image forming units 1M, 1C,1Y, and 1Bk have actually the same constitution, the followingrepresentatively describes details of the magenta image forming unit 1M.

The photoreceptor drum 2 a rotates around its axis. On a circumferencesurface of the photoreceptor drum 2 a, an electrostatic latent image anda toner image are formed. As the photoreceptor drum 2 a, a photoreceptordrum using an amorphous silicon (a-Si)-based material can be employed.The charging roller 3 a uniformly charges the surface of thephotoreceptor drum 2 a. After the charge, the exposure unit 13 exposesthe circumference surface of the photoreceptor drum 2 a, thus formingthe electrostatic latent image.

The developing device 4 a supplies the circumference surface of thephotoreceptor drum 2 a with toner to develop the electrostatic latentimage formed on the photoreceptor drum 2 a. The developing device 4 a isfor two-component developer. The developing device 4 a includes a pairof agitation rollers, a magnetic roller, and a developing roller. Theprimary transfer roller 5 a sandwiches an intermediate transfer belt 7included in the intermediate transfer unit 11 and forms a nip portionwith the photoreceptor drum 2 a. Thus, the toner image on thephotoreceptor drum 2 a is primarily transferred on the intermediatetransfer belt 7. The drum cleaning apparatus 6 a cleans thecircumference surface of the photoreceptor drum 2 a after transfer ofthe toner image.

The intermediate transfer unit 11 includes the intermediate transferbelt 7, a drive roller 8, and a driven roller 9. The intermediatetransfer belt 7 is tightly stretched between the drive roller 8 and thedriven roller 9. Facing and contacting the drive roller 8, a secondarytransfer roller 10 is located. At the proximity of the driven roller 9,a belt cleaning apparatus 71 is located. The drive roller 8 and thesecondary transfer roller 10 form a secondary transfer unit. Thesecondary transfer unit transfers the toner image on the intermediatetransfer belt 7 to a sheet. Several layers of toner images are put onthe intermediate transfer belt 7 from the respective photoreceptor drums2 a, 2 b, 2 c, and 2 d (primary transfer). The secondary transfer unitsecondarily transfers the layered toner images to a sheet supplied fromthe sheet feed cassette 14 or the manual paper feed tray.

The toner containers 12 a, 12 b, 12 c, and 12 d are arranged side byside in a row above the respective image forming units 1M, 1C, 1Y, and1Bk. These toner containers 12 a, 12 b, 12 c, and 12 d store a toner formagenta, a toner for cyan, a toner for yellow, and a toner for black,respectively. The toners with respective colors are supplied to thedeveloping devices 4 a, 4 b, 4 c, and 4 d of the image forming units 1M,1C, 1Y, and 1Bk corresponding to the respective colors of M, C, Y, and Kthrough a supply path (not illustrated).

The exposure unit 13 includes various optical system apparatuses such asa light source, a polygon mirror, a reflective mirror, and a deflectionmirror. The exposure unit 13 irradiates light, which are based on imagedata provided from an external device or a similar device, to thecircumference surfaces of the photoreceptor drums 2 a, 2 b, 2 c, and 2 dprovided to the respective image forming units 1M, 1C, 1Y, and 1Bk, soas to form electrostatic latent images.

The sheet feed cassette 14 houses a sheet bundle formed by lamination ofa plurality of sheets. A pickup roller 15 is located at an upper portionat a right end side of the sheet feed cassette 14. Driving the pickuproller 15 feeds the sheet of the uppermost layer of the sheet bundle inthe sheet feed cassette 14 one by one. At a downstream side of thepickup roller 15, a feed roller 16 and a retard roller 17 are located.The feed roller 16 and the retard roller 17 send out the fed sheet to aconveying path P1.

The conveying path P1 vertically extends at a side portion of the mainbody housing 100. The conveying path P1 is a path for conveying a sheeton which a toner image is to be transferred. The conveying path P1includes a conveyance roller pair 18 and a registration roller pair 19.The conveyance roller pair 18 conveys the sheet. The registration rollerpair 19 supplies the sheet to the secondary transfer unit at apredetermined timing after the registration roller pair 19 causes thesheet to temporarily stand by for correcting skew. At the next to theconveying path P1, an inverting conveying path P2 is formed. Theinverting conveying path P2 is employed for inversely conveying thesheet up to the upstream side of the registration roller pair 19 duringduplex printing. The inverting conveying path P2 includes a plurality ofconveyance roller pairs 20 spaced at appropriate intervals.

A fixing unit 22 and a sheet discharge unit 101 are located at adownstream with respect to the secondary transfer unit in the conveyingpath P1. The fixing unit 22 includes a fixing roller and a pressureroller. The fixing unit 22 heats and pressures the sheet on which thetoner image is secondarily transferred at the secondary transfer unitperforms a fixing process. The sheet discharge unit 101 is locateddownstream of the fixing unit 22. The sheet discharge unit 101 includesa conveyance roller pair 23 and a part of a discharging roller pair 24and conveyance roller pair 20. The sheet discharge unit 101 dischargesthe sheet on which the fixing process is performed from a discharge portof the main body housing 100 to a sheet discharge tray 21.

Subsequently, the following describes an image forming operation by theimage forming apparatus 1 with the above-described constitution. Upon aninstruction signal for starting image formation, the respectivephotoreceptor drums 2 a to 2 d are rotatably driven at the respectiveimage forming units 1M, 1C, 1Y, and 1Bk at a predetermined process speedin the arrow direction in FIG. 1 (clockwise direction). Charging rollers3 a to 3 d uniformly charge these photoreceptor drums 2 a to 2 d. Theexposure unit 13 emits laser beams modulated by color image signals withrespective colors. The exposure unit 13 then irradiates the laser beamsto the surface of the respective photoreceptor drums 2 a to 2 d. Thisforms respective electrostatic latent images corresponding to the colorimage signals with respective colors on the respective photoreceptordrums 2 a to 2 d.

Afterwards, the developing device 4 a supplies the electrostatic latentimage formed on the photoreceptor drum 2 a of the magenta image formingunit 1M with the magenta toner, thus the electrostatic latent imagebecomes a visible image as a magenta toner image. This magenta tonerimage is primarily transferred on the intermediate transfer belt 7rotatably driven in the arrow direction in FIG. 1 at the primarytransfer unit between the photoreceptor drum 2 a and the primarytransfer roller 5 a. Similarly, the cyan image forming unit 1C, theyellow image forming unit 1Y, and the black image forming unit 1Bk alsorespectively form a cyan toner image, a yellow toner image, and a blacktoner image. These toner images are transferred on the intermediatetransfer belt 7 so as to be superimposed on the magenta toner image,which was previously transferred, at the respective primary transferunits. Thus, a full-color toner image is formed on the intermediatetransfer belt 7. The respective drum cleaning apparatuses 6 a to 6 dremove transfer residual toner, which has not been transferred to theintermediate transfer belt 7 and remains on the respective photoreceptordrums 2 a to 2 d.

Then, the registration roller pair 19 conveys the sheet sent out fromthe sheet feed cassette 14 to the conveying path P1 to the secondarytransfer unit at a timing where the top of full color toner image on theintermediate transfer belt 7 reaches the secondary transfer unit betweenthe drive roller 8 and the secondary transfer roller 10. The secondarytransfer roller 10, to which a secondary transfer bias with polarityreverse to the toner is applied, secondarily transfers the full-colortoner image from the intermediate transfer belt 7 to the sheet conveyedto the secondary transfer unit.

Then, the sheet is conveyed to the fixing unit 22, and the full-colortoner image is heated and pressurized, thus the full-color toner imageis heat-fixed on the surface of the sheet. The conveyance roller pair 23and the discharging roller pair 24 of the sheet discharge unit 101discharge the sheet, on which the toner image is fixed, on the sheetdischarge tray 21. The belt cleaning apparatus 71 removes toner that isnot transferred on the sheet and remains on the intermediate transferbelt 7.

The above describes operations of forming an image on one surface of asheet. To form images on both surfaces of a sheet, the sheet dischargeunit 101 reversely conveys the sheet where the image is formed at onesurface through the above-described processes, and then introduces thesheet to the inverting conveying path P2. The conveyance roller pair 20conveys the sheet on the inverting conveying path P2. Then, the sheetwhose front and back are inverted heads for the registration roller pair19. After that, the processes similar to ones described above areperformed on the sheet, thus an image is formed at the reverse surfaceof the sheet.

Next, the following describes the sheet discharge unit 101 in detail.The image forming apparatus 1 with the sheet discharge unit 101 is oneembodiment of the driving apparatus according to the disclosure. FIG. 2illustrates the perspective sheet discharge unit 101. The sheetdischarge unit 101 includes a main body frame 102 made of a resinmaterial, a roller shaft 32, and a drive transmission device 25. Theroller shaft 32 is rotatably supported to the main body frame 102. Oneof the rollers of the conveyance roller pair 20 is integrally mounted tothe roller shaft 32. The drive transmission device 25 is installed toone side portion of the main body frame 102. The drive transmissiondevice 25 includes a stepping motor 27 (a driving motor) and a geargroup. The stepping motor 27 generates rotary driving power. The rotarydriving power generated by the stepping motor 27 is transmitted to theroller shaft 32 via the gear group. Accordingly, the conveyance rollerpair 20 obtains rotational power for conveying the sheet.

FIG. 3 is a perspective view illustrating the drive transmission device25. FIG. 4 illustrates a side of the drive transmission device 25. FIG.5 illustrates a top of the drive transmission device 25. FIG. 6illustrates a cross section of the drive transmission device taken alongthe line VI-VI of FIG. 5. The drive transmission device 25 includes aframe 26 (omitted in FIG. 2), and includes a pinion gear 28 (a drivinginput gear), a reduction gear 29 (a driven gear), and a shaft 30 as theabove-described gear group. The frame 26 is made of sheet metal and towhich the stepping motor 27 is mounted. The pinion gear 28 is directlyconnected to an output rotation shaft 27 a of the stepping motor 27. Thereduction gear 29 is engaged with the pinion gear 28. The shaft 30rotatably supports the reduction gear 29. The reduction gear 29 isengaged with a gear (not illustrated) mounted to an end portion of theroller shaft 32. Besides, the drive transmission device 25 also includesa gear group for inputting driving power to the fixing unit 22; however,the illustration is omitted here. The gear group, which includes thereduction gear 29, is a gear made of a resin material formed by metalmolding.

At the center of the flat-plate-shaped frame 26, a circular through-hole261 is bored. The stepping motor 27 is located at one side of thesurface of the frame 26. The pinion gear 28, the reduction gear 29, andthe shaft 30 are located at the other side of the surface of the frame26. The stepping motor 27 is secured to the frame 26 with three piecesof screws 31 while the output rotation shaft 27 a is aligned with thethrough-hole 261.

The pinion gear 28 is directly connected to the end edge of the outputrotation shaft 27 a of the stepping motor 27. The pinion gear 28includes a columnar rotary drive shaft 28 a and a pinion gear teeth 28G(first gear teeth). Rotary drive power is provided from the outputrotation shaft 27 a to the rotary drive shaft 28 a. The pinion gearteeth 28G are integrally formed at the circumference surface of therotary drive shaft 28 a. The pinion gear teeth 28G have helical gearteeth (first helical teeth). The pinion gear teeth 28G are twistedleftward (a first direction) with respect to an extending direction of ashaft center 28R of the rotary drive shaft 28 a illustrated in FIG. 4 inside view. The columnar shaft 30 has a base end portion 30B secured tothe frame 26. The shaft 30 is a columnar shaft located upright orlocated to protrude from the frame 26 extending parallel to the rotarydrive shaft 28 a.

The reduction gear 29 freely rotates placing the shaft 30 as a rotationshaft. The reduction gear 29 includes reduction gear teeth 29G (secondgear teeth) at the cylindrical outer peripheral surface. The reductiongear teeth 29G also have helical teeth gear (second helical teeth). Thereduction gear teeth 29G are twisted rightward (a second direction) withrespect to an extending direction of a shaft center 30R of the shaft 30in side view. The shaft center 28R of the rotary drive shaft 28 a isparallel to the shaft center 30R of the shaft 30. The pinion gear teeth28G engage the reduction gear teeth 29G at an engaging portion GA withone another. Driving of the stepping motor 27 rotates the pinion gear 28around its shaft. Then, the rotatory power is transmitted to thereduction gear 29 via the engaging portion GA, and the reduction gear 29rotates around the shaft 30.

Next, also with reference to FIG. 7, the following describes a detailedstructure of the reduction gear 29. FIG. 7 illustrates a cross sectionalong an axial direction of the reduction gear 29. The reduction gear 29is, as described above, a gear made of a resin material formed by metalmolding. The reduction gear 29 includes a boss portion 291 with acylindrical body, a rim portion 292, and a web 293. The rim portion 292has a cylindrical body and is concentrically located around the outerperiphery of the boss portion 291. The web 293 connects the boss portion291 and the rim portion 292. The reduction gear teeth 29G are formed atthe outer peripheral surface of the rim portion 292.

The boss portion 291 has a through-hole 29H through which the shaft 30is inserted. The through-hole 29H does not closely fits the shaft 30 andhas an inner diameter slightly greater than an outer diameter of theshaft 30. As described above, since the base end portion 30B of theshaft 30 is secured to the frame 26, the shaft 30 itself does notrotate. Due to a clearance present between the inner wall of thethrough-hole 29H and the outer peripheral wall of the shaft 30, thereduction gear 29 is rotatable with respect to the shaft 30.

The rim portion 292 is a cylindrical body whose axial length isapproximately a half of the length of the boss portion 291. The web 293is a disk-shaped member that connects the outer peripheral surface ofthe boss portion 291 and the one end side (lower end side in FIG. 7) ofthe rim portion 292 in the axial direction. The reduction gear teeth 29Gare formed at a cylindrical region 292B excluding an end edge region292A to which the web 293 is connected among the outer peripheralsurface of the rim portion 292.

When the resin material is metallically molded, assume that a structureto which a disk-shaped body such as a web is connected to the innerperipheral surface of the cylindrical body is to be molded. A wall ofthe cylindrical body is drawn to the disk-shaped body at the connectionpart, likely to generating a concave portion at the outer surface of thecylindrical body (generation of sink mark of resin). This phenomenon isalso true of the end edge region 292A at which the rim portion 292contacts the web 293. The end edge region 292A is easily caved in due tothe sink mark of resin. Regarding such end edge region 292A, avoidingformation of the reduction gear teeth 29G prevents generation of a caveportion at the reduction gear teeth 29G. In this embodiment, the web 293is installed consecutively at the one end side of the rim portion 292 inthe axial direction. Accordingly, even if the reduction gear teeth 29Gis not formed at the region of the rim portion 292 connecting to the web293, the reduction gear teeth 29G with sufficient length can be formedat the outer peripheral surface of the cylindrical region 292B.

FIG. 8 illustrates a cross section along the axial direction of areduction gear 29A (a driven gear) according to a comparative example.The reduction gear 29A includes a boss portion 294 and a rim portion295, which are concentrically located, and a web 296, which connects theboss portion 294 and the rim portion 295. The rim portion 295 hasreduction gear teeth 295G at the outer peripheral surface. The web 296connects the outer peripheral surface of the boss portion 294 and theinner peripheral surface of the rim portion 295 at near the center ofthe rim portion 295 in the axial direction. In the above-describedstructure of the reduction gear 29A, the wall that decreases inthickness by the above-described sink mark of resin causes a part nearthe region of the rim portion 295 connecting to the web 296 to cave in.This generates a caved portion 297 at the center of the reduction gearteeth 295G in the tooth trace direction. In this case, a contact ratioof the reduction gear 29A with respect to the pinion gear 28 becomespoor, causing vibration and noise. The reduction gear 29 of thisembodiment solves this problem. This ensures achieving good engagementof the reduction gear teeth 29G with the pinion gear teeth 28G acrossthe overall length of the reduction gear teeth 29G in the tooth tracedirection.

The rim portion 292 illustrated in FIG. 7 has a tapered shape that has alarge diameter at the one end side to which the web 293 is notconnected, and radially decreases toward the other end side (the endedge region 292A). In association with this, the reduction gear teeth29G also have a similar tapered shape. That is, a teeth height at thetop (the outer diameter part of teeth) of the reduction gear teeth 29Gwith respect to the rim portion 292 is constant in the tooth tracedirection. However, since the rim portion 292 has a tapered shape, theouter diameter of the reduction gear teeth 29G also has a tapered shapein the tooth trace direction.

The tapered shape of the rim portion 292 is induced by a characteristicof shape that the web 293 is connected to the end edge region 292A ofthe rim portion 292. During molding of the reduction gear 29, a shrink(sink mark) is generated toward the center in the radial direction atthe disk-shaped part of the web 293. Accordingly, the end edge region292A of the rim portion 292 is drawn to the center in the radialdirection. Consequently, the rim portion 292 is deformed such that theend edge opposite to the end edge region 292A radially expands tooutside. This deformation yields the tapered shape of the rim portion292 and the reduction gear teeth 29G where the tapered shape radiallydecreases toward the end edge region 292A. This tapered height isapproximately almost several tens micron meters.

As the reduction gear 29A illustrated in FIG. 8, simply connecting theweb 296 to a part near the center of the rim portion 295 in the axialdirection reduces and avoids generation of the tapered shape. However,this case has a failure that the caved portion 297 may be generated atthe reduction gear teeth 295G as described above. Therefore, it ispreferred that the reduction gear teeth 29G be constituted to achievegood engagement with the pinion gear teeth 28G by assuming that the rimportion 292 has a tapered shape.

The rim portion 292 may be tapered intentionally. When the reductiongear 29 is formed by metal molding, it is preferred that a mold taper beprovided to the boss portion 291 and the rim portion 292, which have acylindrical shape, as a draft angle in metal molding. For example, atapered shape caused by the mold taper may be provided to the rimportion 292. Such tapered shapes of the rim portion 292 and thereduction gear teeth 29G may cause a partial contact in engagementbetween the reduction gear teeth 29G and the pinion gear teeth 28G.However, in this embodiment, even if the tapered shape is present,appropriately setting the direction that the helical teeth of thereduction gear teeth 29G and the pinion gear teeth 28G are twisted andthe rotation direction of the pinion gear 28 ensures good engagement ofboth gear teeth. The following describes this point.

With reference to FIG. 3 and FIG. 4, as described above, the pinion gearteeth 28G are helical teeth, and twisted leftward. On the other hand,the reduction gear teeth 29G are also helical teeth but twistedrightward. Here, the output rotation shaft 27 a of the stepping motor 27provides the pinion gear 28 with a rotatory power rotating around theshaft center 28R of the rotary drive shaft 28 a in an anticlockwisedirection R1. Driving the stepping motor 27 to rotate the pinion gear 28in the anticlockwise direction R1 rotates the reduction gear 29, whichengages the pinion gear 28, in a clockwise direction R2. Under suchconditions of the twist direction and the rotation direction of helicalteeth, a thrust power Th is generated on the reduction gear 29. Thethrust power Th acts in a direction away from the stepping motor 27 (thedirection from below to above in FIG. 3 and FIG. 4). This thrust powerTh makes engagement between the pinion gear 28 and the reduction gear 29close to ideal.

FIG. 9 schematically illustrates a state of engagement between thepinion gear 28 and the reduction gear 29 during stop. FIG. 9exaggeratingly draws the tapered shapes of the rim portion 292 and thereduction gear teeth 29G. The cylinder end edge of the tapered shape ofthe rim portion 292 at the side to which the outer peripheral edge ofthe web 293 is not connected has a large diameter. The taper radiallydecreases toward the cylinder end edge at the side to which the outerperipheral edge of the web 293 is connected. A clearance C is presentbetween the inner wall of the through-hole 29H at the boss portion 291of the reduction gear 29 and the outer peripheral wall of the shaft 30(this clearance C is also drawn exaggeratingly). While the pinion gear28 does not rotate, the reduction gear teeth 29G partially contact thepinion gear teeth 28G at the engaging portion GA, where the pinion gear28 engages the reduction gear 29, slightly by an amount of the taper ofthe rim portion 292.

FIG. 10 schematically illustrates a state where the stepping motor 27operates, the pinion gear 28 rotates, and the rotary driving power istransmitted to the reduction gear 29. As described above, by rotation ofthe pinion gear 28 in the anticlockwise direction R1, the reduction gear29 is rotated in the clockwise direction R2, and the thrust power Th isgenerated at the reduction gear 29. This thrust power Th inclines theposture of the reduction gear 29 due to the clearance C as illustratedin FIG. 10.

When the inclination of the reduction gear 29 as described above isgenerated, at the engaging portion GA where the pinion gear 28 engagesthe reduction gear 29, the rim portion 292 with the tapered shapechanges its posture in parallel to the rotary drive shaft 28 a of thepinion gear 28. In view of this, the partial contact between thereduction gear teeth 29G and the pinion gear teeth 28G is solved, thusensuring a high contact ratio of both gear teeth.

According to the above-described driving apparatus of the embodiment,the pinion gear teeth 28G (the first helical teeth), which are helicalteeth gear twisting leftward, engages the reduction gear teeth 29G (thesecond helical teeth), which are helical teeth gear twisting rightward.Transmission of rotary driving power from the pinion gear 28 to thereduction gear 29 generates the thrust power Th. This thrust power Thcauses the reduction gear 29 to swing with respect to the shaft 30 in arange of the clearance C of the boss portion 291. Since the rim portion292 has a tapered shape, the swing causes the rim portion 292 to changeits posture to be parallel to the rotary drive shaft 28 a. Therefore,this makes engagement between the pinion gear teeth 28G and thereduction gear teeth 29G close to ideal engagement. This can solveproblems such as generation of vibration and noise and deterioration ofgears.

Therefore, with the driving apparatus (the image forming apparatus 1)with the stepping motor 27 and the driven gear (the reduction gear 29)made of a resin material, vibration and noise can be reduced as much aspossible. Accordingly, this can achieve reducing noise of these units,also ensuring providing the image forming apparatus 1 without imagequality deterioration caused by vibration. The use of the frame 26 canprovide the driving apparatus to which the stepping motor 27, the piniongear 28, and the reduction gear 29, which are driving sources, areinstalled compactly.

One embodiment of the disclosure is described above in detail; however,the disclosure is not limited to this. For example, the embodiment usesthe exemplary sheet discharge unit 101 is as an example of the drivingapparatus. The driving apparatus may be a driving apparatus for drivingthe photoreceptor drum 2 a, a developing roller, the primary transferroller 5 a, or a similar unit. The image forming apparatus 1 is used asexemplary apparatus to which the driving apparatus is applied; however,the driving apparatus may be applied to an apparatus other than an imageforming apparatus.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

What is claimed is:
 1. A driving apparatus, comprising: a driving motorhaving a motor output rotation shaft; a frame on which the driving motoris mounted; a driving-input pinion gear having a rotary drive shaftdirectly connected to the motor output rotation shaft and having firstgear teeth, the rotary drive shaft therein being configured to receiverotary driving power from the driving motor, the first gear teeth beingintegrally formed with the rotary drive shaft; a columnar shaft providedextending parallel to the rotary drive shaft and protruding from theframe; a driven gear that engages the driving input gear, the drivengear including: a cylindrical boss portion wholly made of a resinmaterial, the boss portion having a through-hole through which thecolumnar shaft is inserted; a tapered rim portion disposedconcentrically with and outer peripherally of the boss portion; secondgear teeth formed on an outer peripheral surface of the rim portion; anda web linking a circumferential surface of the boss portion with the rimportion along one end of the rim portion axially, the web therein beingprovided between the frame and a frame-ward end of the second gearteeth, along a direction perpendicular to the rotary drive shaft and thecolumnar shaft; wherein the first gear teeth are first helical teethtwisting in a first direction with respect to a direction in which therotary drive shaft extends, the second gear teeth are second helicalteeth twisting in a second direction that is the opposite of the firstdirection, the rim portion is tapered, radially decreasing toward theend to which the web is linked, the through-hole in the boss portion hasan inner diameter greater than the columnar shaft outer diameter, andthe rotary drive shaft rotational direction, the first direction, andthe second direction are established such that, with the driven geartilting because of clearance between the through-hole and the columnarshaft, under thrust power generated by engagement between the firsthelical teeth and the second helical teeth and transmission of therotary driving power from the driving input gear to the driven gear, theinclination changes the posture of the tapered rim portion so as toparallel the rotary drive shaft.